Katabatic wind K Katabatic wind A katabatic wind, from the Greek word katabatikos meaning "going downhill", is the technical name for a drainage wind , a wind that carries high density air from a higher elevation down a slope under the force of gravity. Such winds are sometimes also called fall winds. Not all downslope winds are katabatic. For instance, winds such as the Foehn, Chinook or Bergwind, are rain shadow winds where air driven upslope on the windward side of a mountain range drops its moisture and descends leeward drier and warmer. Katabatic winds can rush down elevated slopes at hurricane speeds, but most are not that intense and many are on the order of 10 knots or less. Examples of true katabatic winds include the Mistral in the Mediterranean , the Bora (or Bura) in the Adriatic , the Santa Ana in southern California, and the Oroshi in Japan . Another example is "The Barber," an enhanced katabatic wind that blows over the town of Greymouth in New Zealand when there is a southeast flow over the South Island. It is a wind that is known in the area for its coldness.

A katabatic wind originates from the cooling by radiation of air atop a plateau, a mountain, glacier, or even a hill. Since the density of air increases with lower temperature , the air will flow downwards, warming adiabatically as it descends. The temperature of the wind depends on the temperature in the source region and the amount of descent. In the case of the Santa Ana, for example, the wind can (but does not always) become hot by the time it reaches sea level. In the case of Antarctica, by contrast, the wind is still intensely cold. Katabatic winds are most commonly found blowing out from the large and elevated ice sheets of Antarctica and Greenland . The buildup of high density cold air over the ice sheets and the elevation of the ice sheets brings into play enormous gravitational energy, propelling the winds well over hurricane force. In Greenland these winds are called Piteraq and are most intense whenever a low pressure area approaches the coast. In the Fuegian Archipelago (or Tierra del Fuego ) in South America as well as in Alaska, a wind known as a williwaw is a particular danger to harbouring vessels. It originates in the snow and ice fields of the coastal mountains.

Williwaws commonly blow as high as 100 knots, and 200 knot williwaws have been reported. (Wikipedia) Katabatic wind : definition of Katabatic wind and synonyms of Katabatic wind (English) Theory Sketch of the generation of katabatic winds in Antarctica A katabatic wind originates from radiational cooling of air atop a plateau, a mountain, glacier, or even a hill. Since the density of air is inversely proportional to temperature , the air will flow downwards, warming adiabatically as it descends. The temperature of the wind depends on the temperature in the source region and the amount of descent. In the case of the Santa Ana, for example, the wind can (but does not always) become hot by the time it reaches sea level. In the case of Antarctica, by contrast, the wind is still intensely cold. The entire near-surface wind field over Antarctica is largely determined by the katabatic winds, particularly outside the summer season, except in coastal regions when storms may impose their own windfield.

Impacts Coastal polynyas are produced in the Antarctic by katabatic winds Katabatic winds are most commonly found blowing out from the large and elevated ice sheets of Antarctica and Greenland . The buildup of high density cold air over the ice sheets and the elevation of the ice sheets brings into play enormous gravitational energy. Where these winds are concentrated into restricted areas in the coastal valleys, the winds blow well over hurricane force. [1] In Greenland these winds are called Piteraq and are most intense whenever a low pressure area approaches the coast. In a few regions of continental Antarctica the snow is scoured away by the force of the katabatic winds, leading to "dry valleys" (or " Antarctic oasis ") such as the McMurdo Dry Valleys . Since the katabatic winds are descending, they tend to have a low relative humidity which desiccates the region. Other regions may have a similar but lesser effect, leading to "blue ice" areas where the snow is removed and the surface ice evaporates, but is replenished by glacier flow from upstream.

In the Fuegian Archipelago (or Tierra del Fuego ) in South America as well as in Alaska, a wind known as a williwaw is a particular danger to harbouring vessels. Williwaws originate in the snow and ice fields of the coastal mountains, and while they commonly blow as high as 100 knots, 200-knot williwaws have been reported. [2] See also Sea Monster and Katabatic Winds | Sailing Blog by NauticEd Sailing Blog by NauticEd Posted by Director of Education on February 1, 2013 under Skipper | Comments are off for this article The old tales of sea monsters came ripping back to me as I was experiencing my very own terrifying version. Place – the very beautiful Marlborough Sounds in New Zealand. Well actually not so terrifying and not REALLY a sea monster BUT … it makes for a great start to this story. The day before, my friend Mike and I were walking the famous Queen Charlotte track overlooking Queen Charlotte Sound at the top end of the South Island, New Zealand. We were spending a week boating, fishing, diving, wakeboarding, camping and exploring the Marlborough Sounds – real boy stuff.

We came upon a clearing that allowed us to peer down through the towering native trees into the sound about 1000 feet below and saw something incredibly fascinating. We spent about 20 minutes starring at the effect of katabatic winds blasting down the valleys and exploding into the water. The word exploding is well founded here as we could see the spray flying in to the air each time one of these winds hit the water. I’ve taken the following directly from Wikipedia which describes this effect. Katabatic Wind A katabatic wind, from the Greek word katabatikos meaning “going downhill”, is the technical name for a drainage wind, a wind that carries high density air from a higher elevation down a slope under the force of gravity. Such winds are sometimes also called fall winds. Katabatic winds can rush down elevated slopes at hurricane speeds, but most are not that intense and many are on the order of 10 knots (18 km/h) or less. Not all downslope winds are katabatic.

For instance, winds such as the Foehn, Chinook or Bergwind, are rain shadow winds where air driven upslope on the windward side of a mountain range drops its moisture and descends leeward drier and warmer. Examples of true katabatic winds include the Bora (or Bura) in the Adriatic , the Bohemian Wind or Böhmwind in the Ore Mountains , the Mistral , the Santa Ana in southern California, the Tramontane and the Oroshi in Japan . Another example is “The Barber,” an enhanced katabatic wind that blows over the town of Greymouth in New Zealand when there is a southeast flow over the South Island. It is a wind that is known in the area for its coldness. Theory Right: A Sketch of the generation of katabatic winds in Antarctica A katabatic wind originates from radiational cooling of air atop a plateau, a mountain, glacier, or even a hill. Since the density of air is inversely proportional to temperature, the air will flow downwards, warming adiabatically as it descends. The temperature of the wind depends on the temperature in the source region and the amount of descent.

In the case of the Santa Ana, for example, the wind can (but does not always) become hot by the time it reaches sea level. In the case of Antarctica, by contrast, the wind is still intensely cold. The entire near-surface wind field over Antarctica is largely determined by the katabatic winds, particularly outside the summer season, except in coastal regions when storms may impose their own windfield. Impacts Katabatic winds are most commonly found blowing out from the large and elevated ice sheets of Antarctica and Greenland . The buildup of high density cold air over the ice sheets and the elevation of the ice sheets brings into play enormous gravitational energy. Where these winds are concentrated into restricted areas in the coastal valleys, the winds blow well over hurricane force. [1] In Greenland these winds are called Piteraq and are most intense whenever a low pressure area approaches the coast. In a few regions of continental Antarctica the snow is scoured away by the force of the katabatic winds, leading to “dry valleys” (or “ Antarctic oasis “) such as the McMurdo Dry Valleys . Since the katabatic winds are descending, they tend to have a low relative humidity which desiccates the region.

Other regions may have a similar but lesser effect, leading to “blue ice” areas where the snow is removed and the surface ice evaporates, but is replenished by glacier flow from upstream. In the Fuegian Archipelago (or Tierra del Fuego ) in South America as well as in Alaska, a wind known as a williwaw is a particular danger to harbouring vessels. Williwaws originate in the snow and ice fields of the coastal mountains, and while they commonly blow as high as 100 knots, 200-knot williwaws have been reported. >>>>>>>>>>>> Here is a video we shot of these tubes of wind smashing vertically into the water far below us. Look for the telltale ripples changing the color of the water. Pretty amazing right? So when these winds hit the water traveling at a steep angle it acts like a tube of air hitting the water then expanding out in all 360 degree directions dissipating as the expansion circle grows. So, imagine trying to sail in this? It’s a very frustrating experience and quite possibly dangerous.

You could suffer a serious knock down and depending on the strength crew members could be bashed around and tossed overboard or tossed around in the cabin causing injury. If your boom was not sheeted in, such an instantaneous change in wind direction could cause an automatic gybe bonking hard any crew as the boom raced across. i.e., these winds are really REALLY dangerous. Now back to my sea monster story. So the next day after observing this phenomenon, Miek and I were walking along the beach when one of these winds slammed into the water about 200 ft (65m) in front of us. The force was so hard that water sprayed up into the air about 200 ft then it came ripping at us. A large Gullet type wooden sailboat anchored between us and the impact zone was tossed around like a match stick. Mike ran for the woods like a little girl (hee hee sorry Mike) while I dropped into a rugby scrum pose getting low so I would not be knocked off my feet. Mike got off a photo a second too late as the wind screamed, swirled, gnashed, and gnarled through me whilst making a horrible howling sound.

I would estimate that wind that hit me would have been doing about 65 knots. It lasted for about 2 seconds and was gone. My Sea Monster Here’s Mike’s photo – I’ve added the opaque shape just to help the imagination of the monster but – that was an experience not to be forgotten. One thing is obviously apparent – I would have hated to have my sails up in that. No matter what your experience, THAT would not have been good. So what can you do? Sailing in these types of conditions, I’d be very tempted to drop sails and motor around. Gusts like these at the very least will scare the living daylight out of your crew or worse shred your sails and break some limbs. And the worst is that you’d have only a few seconds of warning. The tip? If you are in windy conditions near mountains or you see this type of phenomena happening, get the sails down. In sailing and boating always expect the unexpected. Perhaps now you can begin to believe the origins of a few sea monster stories. Raaaaaar Other than that – the Marlborough Sounds in New Zealand is something not to be missed in a lifetime.

View this 360 panorama below I took of Ships Cove at the top end of Queen Charlotte Sound. Captain Cook spent many months here on his 3 world trips using the bay to rest, reprovision, reseal and repair his boats. View the interactive panorama here. Take NauticEd Online Sailing Courses to get more sailing tips and tricks and the world’s most advanced sailing certification. My HeaRT iS ReD... NoT PiNK!!!: SuB GLoBaL SiSTeM aNGiN TeMPaTaN SuB GLoBaL SiSTeM aNGiN TeMPaTaN 1.0 Pengenalan Menurut De Blij (2004), beliau mendefinisikan angin sebagai: ‘ wind is the movement of air relative to the Earth’s surface, is a response to an imbalance of forces acting on air molecules. This is true whether the air moving horizontally or vertically, and indeed these two movement dimension are related via the concept of atmospheric pressure.’ (H.J. de Blij, Peter O. Muller, dan Richard S.

Williams, Jr, 2004) Oleh itu, Angin ialah udara yang bergerak yang diakibatkan oleh putaran bumi ( kesan Coriolis ) dan juga pemanasan tidak sekata permukaan bumi yang mengakibatkan perbezaan tekanan udara (tekanan tinggi ke tekanan rendah) di sekitarnya. Masa dan skala angin berbeza-beza, dari bayu setempat selama beberapa minit hinggalah angin sejagat selama beberapa hari. ( ,2008) Apabila dipanaskan, udara mengembang. Udara yang telah mengembang menjadi lebih ringan sehingga naik. Apabila hal ini terjadi, tekanan udara turun kerana udaranya berkurang. Udara dingin di sekitarnya mengalir ke tempat yang bertekanan rendah tadi. Udara yang naik tadi menyusut menjadi lebih berat dan turun ke tanah. Di atas tanah udara menjadi panas lagi dan naik kembali.

Aliran naiknya udara panas dan turunnya udara dingin ini dinamakan perolakan . Sistem angin boleh dibahagikan kepada dua bahagian iaitu Sistem Angin Berskala ( besar dan kecil) dan Sistem Angin Tempatan. Namun dalam kajian ini, tumpuan diberikan kepada Sistem angin tempatan dan pecahannya. 2.0 Sistem Angin Tempatan Menurut De Blij (2004), sistem angin tempatan adalah lebih sesuai dalam cuaca harian kerana ia lebih banyak bertindakbalas terhadap perbezaan-perbezaan halus dalam tekanan atmosfera. Hal ini boleh digambarkan melalui penyataan di bawah ‘Although we cannot overlook the forces outlined in the preceding when we focus our attention on small-scale air flows, local wind system are often more significant in day-to-day weather because they respond to much more subtle variations in atmospheric pressure than are depicted in Fig.9.9. Moreover, because smaller distances are involved, the effect of the Coriolis force can usually be disregarded.

A number of common local wind system serve to illustrate how topography and surface type can influence the pressure gradient and its resultant wind flow.’ Sistem angin tempatan boleh dibahagikan kepada beberapa jenis angin iaitu Bayu Laut dan Bayu Darat, angin gunung dan angin lembah, angin katabatik, angin anabatik dan angin fohn.. 2.1 Bayu Laut dan Bayu Darat Di seluruh kawasan di dunia didapati terdapat pelbagai jenis angin tempatan yang mempunyai pelbagai jenis nama. Antara angin tempatan yang paling terkemuka adalah Bayu Darat dan Bayu Laut. Bayu Darat dan Bayu Laut terjadi disebabkan terdapat perbezaan sifat diantara daratan dan lautan dalam menyerap dan melepaskan tenaga panas matahari. Bahagian daratan ternyata menyerap dan melepaskan tenaga panas matahari dengan lebih cepat berbanding lautan.

Menurut Wikipedia, terdapat pandangan daripada beberapa tokoh mengenai kejadian Bayu Laut dan Bayu Darat. Hal ini boleh digambarkan dalam petikan dibawah. ‘The ancient Greeks were the first to write extensively of the sea-land breeze rhythm. Homer, in the Odyssey, related that both Odysseus and Telemachus set sail after dark to take advantage of the land breeze blowing out to sea. Plutarch spoke of the Athenian commander Themistocles using the onset of the sea breeze, which produced rough seas in the Bay of Salamis, to defeat the Persian fleet. Persian ships could not be maneuvered in the rough seas as well as the smaller ones that were used by the Greeks, thus giving the Greeks the decisive tactical advantage. Aristotle in Problemata and Theophratus in On the Winds attempted to describe the genesis and nature of the land and sea breezes. They both considered the land breeze to be the dominant partner and the sea breeze only the reflection of the land breeze off obstacles such as islands and coastal hills.

They believed that the alternating current, as they called the sea breeze, could not blow across the open sea where no obstacles from which to rebound existed.’ (Keith C. Heidorn, 1998 dalam ) Menurut De Blij (2004) pula dalam bukunya Physical Geography, The Global Environtment, beliau menjelaskan tentang Sistem Bayu Laut dan Sistem Bayu Darat. Hal ini dapat digambarkan melalui petikan dibawah: ‘During the day a land surface heats up quicckly, and the air layer in contact with it rises in responseto the increased air temperature. This rising air produces a low-pressure cell over the coastal land or island. Since the air over the adjacent water is cooler, it subsides to produce a surface high-pressure cell. A pressure gradient is thereby produced, and air in contact with the surface now moves from high pressure to low pressure. Thus during the day, shore-zone areas generally experience air moving from water to land that is called a sea breeze(Fig.2.1.1A).

At night, when the temperature above the land surface has dropped sufficiently, the circulation reverse because the warmer air (and lower pressure) is now over the water. This results in air moving from land to water and its called a land breez(FIG.2.1.1B)’ (H.J. de Blij, Peter O. Muller, dan Richard S. Williams, Jr 2004:115) Rajah 2.1.1: Sistem Sirkulasi Bayu Laut (A) dan Bayu Darat (B) (Sumber: H.J. de Blij, Peter O. Muller, dan Richard S. Williams, Jr 2004:115) Bayu Darat bertiup pada waktu malam dan Bayu Laut bertiup pada waktu siang. Bayu Darat terjadi ketika pada malam hari tenaga panas yang diserap permukaan bumi sepanjang hari akan dilepaskan lebih cepat oleh daratan (udara dingin). Sementara itu di lautan tenaga panas sedang dalam proses dilepaskan ke udara.

Gerakan konvektif tersebut menyebabkan udara dingin dari daratan bergerak menggantikan udara yang naik di lautan sehingga terjadi aliran udara dari darat ke laut. Bayu darat terjadi pada tengah malam dan awal pagi. Bayu Laut terjadi ketika pada pagi hingga menjelang tengahari, daratan menyerap tenaga panas lebih cepat dari lautan sehingga suhu udara di darat lebih panas daripada di laut. Akibatnya udara panas di daratan akan naik dan digantikan udara sejuk dari lautan. Maka terjadilah aliran udara dari laut ke darat. Bayu laut terjadi pada tengahari dan malam hari. (Rajah 2.1.2) Rajah 2.1.2: Bayu Darat (a) dan Bayu Laut (b) Sumber http: Bayu Laut terjadi di daerah pantai. Pada siang hari daratan lebih cepat menerima panas dibandingkan dengan lautan.

Angin bertiup dari laut ke darat, disebut Bayu Laut Sebaliknya, pada malam hari daratan lebih cepat melepaskan panas dibandingkan dengan lautan. Daratan bertekanan maksimum dan lautan bertekanan minimum. Angin bertiup dari darat ke laut, disebut Bayu Darat . (Rajah 2.1.3) Rajah 2.1.3: Bayu Laut (A) dan Bayu Darat (B) (Sumber: " ) Malaysia adalah sebuah negara yang dikelilingi laut. Oleh itu, kesan bayu laut dan bayu darat ke atas corak tiupan angin adalah besar, terutamanya semasa hari tidak berawan. Pada keadaan petang yang terang cahaya matahari, bayu laut dengan kelajuan antara 10 dan 15 knot selalunya terjadi dan bayu ini boleh mencapai beberapa puluh kilometer ke dalam kawasan pendalaman.

Dalam keadaan malam langit terang, proses sebaliknya berlaku di mana bayu darat yang lebih lemah kelajuannya boleh terjadi di kawasan pantai. ( ). Berdasarkan petikan yang diambil daripada wikipedia, 2007 pula. Terdapat penyataan lain tentang konsep Bayu Laut dan Bayu Darat. Hal ini boleh digambarkan dalam petikan dibawah: ‘Differential heating is the motive force behind land breezes and sea breezes (or, in the case of larger lakes, lake breezes), also known as on- or off-shore winds. Land absorbs and radiates heat faster than water, but water releases heat over a longer period of time. The result is that, in locations where sea and land meet, heat absorbed over the day will be radiated more quickly by the land at night, cooling the air. Over the sea, heat is still being released into the air at night, which rises. This convective motion draws the cool land air in to replace the rising air, resulting in a land breeze in the late night and early morning. During the day, the roles are reversed.

Warm air over the land rises, pulling cool air in from the sea to replace it, giving a sea breeze during the afternoon and evening’. ( Diperoleh daripada ) 2.2 Angin gunung dan angin lembah Menurut De Blij (2004) dalam bukunya Physical Geography, The Global Environtment, beliau menjelaskan tentang Sistem Angin Gunung dan Angin Lembah. Hal ini dapat digambarkan melalui petikan dibawah: ‘Mountain slopes, too, are subject to the reversal of day and night local circulation system. This wind circulation is also thermal, meaning that it is driven by temperature differences between adjacent topographic features. During the day, mountain terrain facing the Sun tends to heat up more rapidly than do shadowed, surrounding slopes. This caused low pressure to developed, spawing an upsloping valley breeze. At night, greater radiativeloss from the mountainslopes cools them more sharply, high pressure develops, and a downslopinh mountain breeze results’. (H.J. de Blij, Peter O. Muller, dan Richard S.

Williams, Jr 2004:115) Menurut Wikipedia (2007) pula, Angin Gunung dan Angin lembah boleh dijelaskan seperti dalam petikan dibawah: ‘ Mountain breezes and valley breezes are due to a combination of differential heating and geometry. When the sun rises, it is the tops of the mountain peaks which receive first light, and as the day progresses, the mountain slopes take on a greater heat load than the valleys. This results in a temperature inequality between the two, and as warm air rises off the slopes, cool air moves up out of the valleys to replace it. This upslope wind is called a valley breeze. The opposite effect takes place in the afternoon, as the valley radiates heat. The peaks, long since cooled[, transport air into the valley in a process that is partly gravitational and partly convective and is called a mountain breeze’. ( Diperoleh daripada ) Pada siang hari puncak gunung lebih cepat menerima panas daripada lembah yang dalam keadaan tertutup.

Puncak gunung tekanan udaranya minimum dan lembah tekanan udaranya maksimum. Kerana keadaan ini maka udara bergerak dari lembah menyusur lereng menuju ke puncak gunung. Angin dari lembah ini disebut angin lembah. Pada siang hari udara yang seolah-olah terkurung pada dasar lembah lebih cepat panas dibandingkan dengan udara di puncak gunung yang lebih terbuka (bebas), maka udara mengalir dari lembah ke puncak gunung menjadi angin lembah. Sebaliknya pada malam hari udara mengalir dari gunung ke lembah menjadi angin gunung. Rajah 2.2.1: Bagaimana terjadinya (a) angin lembah dan (b) angin gunung Sumber, Pada malam hari puncak gunung lebih cepat mengeluarkan panas daripada lembah.

Akibatnya di puncak gunung bertekanan lebih tinggi (maksimum) dibandingkan dengan di lembah (minimum) sehingga angin bertiup dari puncak gunung menuruni lereng menuju ke lembah. Angin dari puncak gunung ini disebut angin gunung. Angin lembah terjadi ketika matahari terbit, puncak gunung adalah daerah yang pertama kali mendapat panas dan sepanjang hari selama proses tersebut, lereng gunung mendapat energi panas lebih banyak daripada lembah. Sehingga menyebabkan perbedaan suhu antara keduanya. Udara panas dari lereng gunung naik dan digantikan dengan udara dingin dari lembah. Akibatnya terjadi aliran udara dari lembah menuju gunung. Sedangkan pada tengahari lembah akan melepaskan tenaga panas dan puncak gunung yang telah mendingin akan mengalirkan udara ke lembah. Aliran udara tersebut dinamakan angin gunung.

2.3 Angin anabatik Angin anabatik adalah angin yang menaiki lereng gunung ke atas pada siang hari, terutama sebelum tengah hari. Hal ini disebabkan oleh suhu udara pada lereng lebih tinggi daripada suhu udara pada ketinggian yang sama berjarak agak jauh dari lereng. Karena datangnya dari arah lembah angin ini disebut pula angin lembah. ( Bayu lurah (angin anabatik) adalah bertentangan dengan angin gunung. Pada waktu siang, pemanasan lurah-lurah gunung oleh sinaran matahari akan menyebabkan udara menjadi panas dan kemudian naik ke atas mengikut cerun gunung hingga ke puncak gunung. Udara panas yang naik ke atas semakin menjadi sejuk melalui penyejukan adiabatik dan kemudian menghasilkan awan kumulus serta hujan lebat (Rajah di bawah).

Rajah2.3.1: Bayu LurahSumber, Berdasarkan artikel yang diambil daripada wikipedia, 2006 pula, penerangan tentang Angin anabatik boleh dilihat melalui petikan dibawah: ‘An anabatic wind, from the Greek anabatos, verbal of anabainein meaning moving upward, is a wind which blows up a steep slope or mountain side. It is also known as an upslope flow. These winds typically occur during the daytime in calm sunny weather. A hill or mountain top will be radiatively warmed by the Sun which in turn heats the air just above it. Air at a similar altitude over an adjacent valley or plain does not get warmed so much because of the greater distance to the ground below it. The effect may be enhanced if the lower lying ground is shaded by the mountain and so receives less heat. The air over the hill top is now warmer than the air at a similar altitude around it and will rise through convection . This creates a lower pressure region into which the air at the bottom of the slope flows, causing the wind.

It is common for the air rising from the tops of large mountains to reach a height where it cools adiabatically to below its dew point and forms cumulus clouds . These can then produce rain or even thunderstorms . Anabatic winds are particularly useful to soaring glider pilots who can use them to increase the aircraft's altitude, though detrimental to the maximum downhill speed of cyclists’. (Diperoleh daripada, , 2006) 2.4 Angin Katabatik Menurut McKnight, TL & Hess, Darrel (2000) dalam Wikipedia 2008, beliau menjelaskan asal usul istilah Angin Katabatik. Hal ini boleh dilihat melalui petikan dibawah. ’A katabatic wind, from the Greek word katabatikos meaning "going downhill", is the technical name for a drainage wind , a wind that carries high density air from a higher elevation down a slope under the force of gravity.

Such winds are sometimes also called fall winds.’ (McKnight, TL & Hess, Darrel (2000:131-2) dalam ) Pembentukan Angin Katabatik (Sumber, 2.4.1: ) Angin katabatik adalah hampir sama dengan angin gunung kecuali angin katabatik dihasilkan oleh tarikan graviti (jadi amat susah untuk membezakan angin gunung daripada angin katabatik sebab kedua-duanya mengalir dari cerun atas ke cerun bawah). Udara yang sejuk lagi tumpat di puncak gunung atau dataran tinggi adalah lebih berat lalu ditarik ke cerun bawah oleh daya graviti bumi.

Contohnya angin katabatik ialah angin mistral (Bahasa Perancis) dan angin bora (Bahasa Yugoslavia) (Rajah di bawah) Rajah 2.1.1 Angin KatabatikSumber: Kawasan-kawasan yang terletak di pinggir gurun sentiasa mengalami angin panas dan kering yang bertiup dari gurun. Misalnya, angin panas yang bertiup dari Gurun Sahara ke arah utara dan mempengaruhi pantai Mediterranean dikenali sebagai angin siroko. Angin panas dan kering ini merupakan bencana sebab ia memusnahkan tanaman buah-buahan sitrus. Di Mesir, angin ini dikenali sebagai angin kamsin dan diberikan nama angin leveci di Sepanyol. Berdasarkan Wikipedia, Proses pembentukan Angin katabatik dijelaskan dengan lebih teliti dalam petikan dibawah: ’A katabatic wind originates from the cooling by radiation of air atop a plateau, a mountain, glacier, or even a hill.

Since the density of air increases with lower temperature , the air will flow downwards, warming adiabatically as it descends. The temperature of the wind depends on the temperature in the source region and the amount of descent. In the case of the Santa Ana, for example, the wind can (but not always) become hot by the time it reaches sea level. In the case of Antarctica, by contrast, the wind is intensely cold. Katabatic winds are most commonly found blowing out from the large and elevated ice sheets of Antarctica and Greenland . The buildup of high density cold air over the ice sheets and the elevation of the ice sheets brings into play enormous gravitational energy, propelling the winds well over hurricane force. In Greenland these winds are called Pitaraq and are most intense whenever a low pressure area approaches the coast. In the Fuegian Archipelago (or Tierra del Fuego ) in South America as well as in Alaska, a wind known as a williwaw is a particular danger to harbouring vessels. It originates in the snow and ice fields of the coastal mountains. Williwaws commonly blow as high as 100 knots, and 200 knot williwaws have been reported.

Mountain breezes are one example of what's known more generally as a katabatic wind . These are winds driven by cold air flowing down a slope, and occur on the largest scale in Greenland and Antarctica (fig. . Most often, this term refers to winds which form when air which has cooled over a high, cold plateau, is set in motion and descends, under the influence of gravity. Winds of this type are common in regions of Mongolia and in glaciated locations. Because katabatic refers specifically to the vertical motion of the wind, this group also includes winds which form on the lee side of mountains, and heat as a consequence of compression. Such winds may undergo a temperature increase of 20 °C (68 °F ) or more, and many of the world's "named" winds belong to this group.

Among the most well-known of these winds are the chinook of Western Canada and the American Northwest, the Swiss foehn , California's infamous Santa Ana wind , and the French Mistral .’ (McKnight, TL & Hess, Darrel (2000:131-2) dalam ) Rajah 2.4.2: Angin katabatik di Antartika Sumber, Antara contoh angin katabatik yang terdapat dalam dunia termasuklah Mistral di Mediterranean, Bora (atau Bura) di Adriatik, Santa Ana di California selatan, dan Oroshi di Jepun. 2.5 Angin Fohn Angin Fohn adalah angin yang bertiup di bahagian belakang atau di bagian bawah angin gunung atau pegunungan dengan sifat panas, kering, kencang dan ribut. Hal ini disebabkan oleh udara yang dipaksa secara mekanik menaiki dan melewati puncak dan kemudian menuruni lereng bagian belakang gunung.

Udara yang turun ini mengalami pemanasan adiabatik. Angin fohn dan angin cinuk merupakan angin tempatan yang dipengaruhi oleh bentuk muka bumi. Angin fohn dan angin cinuk yang kering lagi panas terjadi di cerun banjaran gunung yang terlindung. Angin-angin ini dihasilkan daripada percampuran lapisan udara atas dan bawah secara turbulens di cerun yang terlindung itu. Lapisan udara atas yang mengandungi sedikit lembapan akan dikeringkan dan dipanaskan apabila ia mengalir ke aras yang rendah. Angin fohn berlaku di Banjaran Alps di Eropah sementara angin cinuk berlaku di Banjaran Rocky di Amerika Utara. Bagi angin cinuk, ia mula berasal dari pantai barat Amerika Utara.

Angin baratan ini bertiup dari Lautan Pasifik dan membawa hujan lebat ke pantai barat dan cerun barat (cerun yang menghadap angin) Banjaran Rocky. Selepas angin ini merentasi puncak Banjaran Rocky dan sampai ke cerun timur (cerun terlindung), ia sudah menjadi kering (Rajah di bawah). Rajah 2.5.1: Angin CinukSumber, Menurut McKnight, TL & Hess, Darrel (2000) dalamWikipedia 2008, Angin Jatuh atau Fohn ialah angin jatuh bersifatnya kering dan panas terdapat di lereng pegunungan Alpine. Sejenis angin ini banyak terdapat di Indonesia dengan nama angin Bahorok (Deli), angin Kumbang (Cirebon), angin Gending di Pasuruan (Jawa Timur), dan Angin Brubu di Sulawesi Selatan).

Angin fohn atau angin lokal atau angin terjun adalah angin yang terjadi apabila ada gerakan massa udara yang menaiki suatu pegunungan dengan ketinggian lebih dari 200 meter. Massa udara yang mencapai puncak pegunungan akan mengalami kondensasi dan akhirnya timbul hujan pada satu sisi lereng . Adapun pada lereng yang lain tidak terjadi hujan karena terhalang tingginya pegunungan. Daerah yg tidak mengalami hujan disebut daerah bayangan hujan . Rajah2.5.2: Bagaimana Angin Fohn Berlaku Sumber, Pada daerah bayangan hujan itu angin dari atas pegunungan akan bergerak menuruni lereng pegunungan dengan kecepatan tinggi. Hal itu menyebabkan naiknya suhu udara , karena setiap turun 100 meter udara naik 1°C. Dengan demikian angin yang turun bersifat panas dan kering.

Angin itulah yang disebut angin fohn. Antara contoh Angin fohn yang terjadi di Indonesia adalah seperti Angin Bohorok, Angin Kumbang, Angin Gending, Angin Brubu, dan Angin Wambraw ( ) 2.6 Lain-lain Sistem Angin Tempatan. Menurut Wikipedia, 2008, masih terdapat sistem angin tempatan yang lain tetapi tidak diperjelaskan. Hal ini dapat dilihat melalui petikan dibawah: ‘A widely-used term, though one not formally recognised by meteorologists, is orographic wind. This refers to air which undergoes orographic lifting.

Most often, this is in the context of winds such as the chinook or the föhn, which undergo lifting by mountain ranges before descending and warming on the lee side.’ (McKnight, TL & Hess, Darrel (2000:131-2) dalam ) 3.0 Penutup Kesimpulannya, Sistem Angin tempatan dapat dibahagikan kepada lima pecahan utama iaitu Bayu Laut dan Bayu Darat, Angin Gunung dan Angin Lembah, Angin Katabatik, Angin Anabatik dan Angin Fohn manakala terdapat juga jenis angin lain namun masih belum dibincangkan secaras terperinci. Menurut De Blij 2004, beliau menyatakan bahawa kadangkala Sistem Angin Tempatan dilihat lebih menonjol daripada Sistem Angin Berskala. Hal ini boleh dilihat melalui petikan dibawah: ‘In many locations, as we have just seen, local winds can at times become more prominent than larger-scale airflows.

But the regionals expression of the global system of wind currents still play a far more important role overall’. (H.J. de Blij, Peter O. Muller, dan Richard S. Williams, Jr, 2004:117) BIBLIOGRAFI H.J. de Blij, Peter O. Muller, dan Richard S. Williams, Jr, Physical Geography, The Global Environment, Third Edition. New York:Oxford University Anabatic wind (2008). Diperoleh daripada " " Angin Fohn. Diperoleh pada Ogos 30 daripada " " Angin (2008), Diperoleh pada Ogos 30 daripada " ” Bayu Laut dan Bayu Darat (2008)Diperoleh pada Ogos 30 daripada Brown, Dan (2001). Katabatic Winds., "Deception Point", pp. 197 Foehn wind (2008). Diperoleh pada Ogos 30 daripada " " Katabatic wind (2008).

Diperoleh pada Ogos 30 daripada " " : see@islandnet.com . Land breeze(2007). Diperoleh pada Ogos 30 daripada “” McKnight, TL & Hess, Darrel (2000). Foehn/Chinoonk Winds. In , Physical Geography: A Landscape Appreciation, pp. 132. Upper Saddle River, NJ: Prentice Hall. McKnight, TL & Hess, Darrel (2000). Katabatic Winds. In , Physical Geography: A Landscape Appreciation, pp. 131-2. Upper Saddle River, NJ: Prentice Hall. Sea breeze(2008). Diperoleh pada Ogos 30 daripada Wind(2008). Diperoleh pada Ogos 30 daripada " " iLLuSTRiaTe BY ೊ۩ೊ sHu_MaNsHu ೊ۩ೊ iN THe MoMeNT oF 5:23 AM

Question: From the Greek for 'going downhill' and most commonly found in Antarctica and Greenland, what is the name of the wind that carries high density air from a higher elevation down a slope under the force of gravity?
Answer: Katabatic wind